1. Field of the Invention
The present invention is directed to an anchor for use in either a friable material, particularly to a self-drilling anchor to be used in drywall mounted to a member or in a relatively thin semi-rigid material such as a hollow door.
2. Description of the Related Art
Because drywall is a friable material, mounting articles thereto can be difficult. In the past, at least three methods have been used. For light weight articles, small plastic expansion anchors have been used. These expansion anchors have typically required three steps to install: first, a hole is drilled into the drywall; second, the anchor insert is driven into the drilled hole; and finally, a threaded fastener is advanced into the anchor, spreading the anchor into engagement with the drywall. However, expansion anchors can typically hold light loads only.
For heavy duty applications, toggle bolts have been used. While toggle bolts have been effective, they are also generally expensive because they involve parts which must move relative to one another. Toggle bolts also have been known to be difficult to install.
Self-drilling anchors for mounting heavier loads also have been used. These self-drilling anchors typically are installed by drilling into the drywall with the anchor itself. The anchor also includes threading having a high thread height to provide a high pullout in the drywall. Examples of self-drilling anchors include the anchor sold under the trademark E-Z ANCOR manufactured by ITW Buildex, and those disclosed in U.S. Pat. Nos. 4,601,625, 5,190,425, and 5,558,479, all of which are assigned to the assignee of this application.
Self-drilling anchors have proved effective for holding higher loads when installed in drywall alone. However, in most cases the drywall is mounted to wood support members, or studs, that are unseen by the user, and typically the location of these support members are unknown and unchecked by the user. When a user of a typical self-drilling fastener attempts to install the anchor in drywall at a location of a support member, the anchor is unable to drill into the support member, causing the anchor to spin in place so that the anchor's high threading strips out the drywall, resulting in failure of the anchor and creating an unsightly scar on the wall. Even if the anchor is able to drill into the support member slightly, the anchors have been known to tightly engage the support member and break due to torsion on the anchor.
Drywall anchors typically have a head or flange that is larger than the outer diameter of the drywall threading to prevent the anchor from being driven through the drywall as the anchor is installed. However, large anchor heads have been known to displace drywall as the anchors are driven, causing drywall at the surface to bulge up around the anchor, conventionally referred to as blistering of the drywall. The large outer diameter of the drywall threading may also cause displacement of drywall leading to blistering. Blistering creates puffing at the drywall surface which is unsightly and unappealing and may make it difficult to mount some articles to drywall so that the article is flush with the drywall surface.
Mounting self-drilling anchors to relatively thin semi-rigid materials such as a veneered panel of a hollow door can also be difficult. The small thickness of the material and the splintering caused during driving may significantly reduce the holding strength of the anchor.
What is needed is a self-drilling anchor for use in a variety of substrates such as drywall or hollow doors that reduces drywall blistering or securely fastens to the hollow door without reducing holding strength.